1. Field of the Invention
The present invention relates to a method of expressing a gray level of a high load image and a driving apparatus for a Plasma Display Panel (hereinafter, referred to as a PDP) using the method, and more particularly, to a method of expressing a gray level of a high load image and a PDP driving apparatus using the method that improves the characteristics to express a low gray level in displaying the high load image.
2. Description of the Related Art
A PDP is a display device that displays image data inputted as an electrical signal by selectively illuminating discharge cells arranged in a matrix form.
Such a PDP should be able to express gray levels in order to function as a color display device, and a gray level expressing method by time-division control of a plurality of subfields created by the division of one field is employed to realize the gray level expression.
Since the PDP consumes a great deal of electrical power, Automatic Power Control (hereinafter referred to as APC) technology is used to control the power consumption according to the average signal level or a load ratio of a frame to be displayed. In the APC technology, APC levels are changed according to the load ratio of the image data corresponding to the input image, and the power consumption is confined to a certain level while the number of sustain pulses is changed at every APC level.
In general, according to the APC technology, as the load ratio of the input image decreases, the power consumption decreases and therefore a relatively large number of sustain pulses can be used, and accordingly, the number of sustain pulses assigned to the respective subfields also increases. On the contrary, as the load ratio of the input image increases, the power consumption increases and a relatively small number of sustain pulses must be used to reduce the power consumption, and accordingly, the number of sustain pulses assigned to the respective subfields also decreases.
In order to express a gray level of the image of a low load, one sustain pulse is assigned to a subfield SF0 of the lowest significance, i.e. the least significant bit (LSB) subfield, four sustain pulses are assigned to a subfield SF1 of the second lowest significance, i.e. a 2nd LSB subfield, and eight and sixteen sustain pulses are respectively assigned to a subfield SF2 of the third lowest significance, i.e. a 3rd LSB subfield, and a subfield SF3 of the fourth lowest significance, i.e. a 4th LSB subfield. In such a situation, the number of sustain pulses varies according to the APC level.
When the gray level is 0, the illuminating amount is also 0 as there is no mapped subfield. However, when the gray level is 1, the LSB subfield SF0 is mapped and the illuminating amount in that situation is determined by the sum of the illuminating amount 1addr corresponding to one address section and the illuminating amount 1sus by one sustain pulse. Furthermore, when the gray level is 2, the second LSB subfield SF1 is mapped, and the illuminating amount is determined by the sum of the illuminating amount 1addr corresponding to one address section and the illuminating amount 4sus by four sustain pulses. Moreover, the gray level 3 is mapped to the second LSB subfield SF1, and the illuminating amount is determined by 1addr+5sus. Other gray levels are mapped according to such a manner, and the illuminating amounts are determined by the mapped subfields.
The illuminating amount determined by the subfield mapping of every gray level, especially the illuminating amount determined at the low gray levels from 0 to 4, increases gradually as the gray level increases. Therefore, it can be understood that the linearity of gray level is maintained in the case of low load image.
In the case of a high load image of a PDP, the number of sustain pulses assigned to all subfields decreases for the suppression of the power consumption at the high load image, and in such a situation, one sustain pulse is assigned to the LSB subfield SF0 as well as to the 2nd LSB subfield SF1 for the expression of gray level of the corresponding image, and four and eight sustain pulses are respectively assigned to the 3rd LSB subfield SF2 and 4th LSB subfield SF3. In that situation, the number of sustain pulses assigned to the respective subfields are converted according to the APC level.
When the gray level is 0, the illuminating amount is also 0 as there is no mapped subfield. However, the gray level of 1 is mapped to the LSB subfield SF0 and the illuminating amount in that situation is determined by 1addr+1sus, the gray level 2 is mapped to the second LSB subfield SF1 and the illuminating amount in that situation is determined by 1addr+1sus, and the gray level 3 is mapped to the LSB subfield SF0 and the 2nd LSB subfield SF1 and the illuminating amount in that situation is determined by 2addr+2sus. Other gray levels are mapped according to such a manner, and the illuminating amounts are determined by the mapped subfields.
The illuminating amount determined by the subfield mapping of every gray level, especially the illuminating amount determined at the low gray levels from 0 to 4, does not increase gradually as the gray level increases. Comparing gray level 1 with gray level 2, even though the gray level increases, the illuminating amount does not increases since the number of sustain pulses assigned to the LSB subfield and the 2nd LSB subfield are identical to each other. Furthermore, comparing the gray level 2 with gray level 3, the increment of illuminating amount at the gray levels is relatively small even through the gray level increases gradually. The illuminating amount does not increase at all or increases a little even through the gray level increases such as from gray level 1 to gray level 3, so the gray level can not be expressed properly in expressing the low gray level at the high load image.
In the PDP described above, the number of sustain pulses is reduced to lower the power consumption at the high load image when the APC technology is adopted, which can cause a deterioration of the linearity of the gray level when the number of sustain pulses becomes extremely low or the integral multiple number of sustain mapping cannot be formed, and therefore causes a breakdown in expressing the gray level.